Researchers have sequenced the oldest known DNA in the world. Using material from the early and middle Pleistocene subepochs, ancient DNA analysis breaks the world’s oldest sequenced DNA record. It comes from mammoth remains that were discovered in Siberian permafrost and shows that in the right conditions the ancient DNA tin survive more than a million years.
But the analysis of such ancient DNA depends on researchers having the right technology as well. Fortunately, an international team led by researchers from the Paleogenetics Center in Stockholm (Sweden) had at their disposal advanced sequencing and bioinformatics technology. A Nature The new article’s report says researchers pushed the current technology almost to its limits to allow the extraction of ancient DNA strands from mammoth teeth that had been preserved in Siberian permafrost. The senior author of the Nature study, Love Dalén, a professor of evolutionary genetics at the Center for Paleogenetics, notes that the scientific team has been lucky, saying:
“It’s not that everything in permafrost always works. The vast majority of samples have shitty DNA. ”
How the ancient Mammoth’s DNA has broken records
The discovery is truly amazing because after an organism dies, its chromosomes become smaller and smaller, and in most cases, extremely old DNA strands have become so small that they have lost all their informative content. . But a new article published in the magazine Nature shows that the team has obtained 49 million base pairs of nuclear DNA from a 1.65 million-year-old tooth found near a village called Krestovka (the tooth has also been called Krestovka ). They also extracted 884 million base pairs of ancient DNA from a 1.3 million-year-old tooth known as Adycha and 3.7 billion base pairs of DNA from a 600,000-year-old woolly mammoth tooth. which they have called Chukochya. The three mammoth remains were discovered in the 1970s and are part of the collection of the Russian Academy of Sciences in Moscow.
Love Dalén and lead co-author Patrícia Pečnerová with a huge tusk on Wrangel Island. (Credit: Gleb Danilov)
He Nature A news report explains that the ancient study of mammoth DNA has not discovered the oldest biomolecular information from the fossil record, which is a protein sequenced in 2016 from 3.8 million ostrich eggshells years of Tanzania. Second, there is a 1.77 million-year-old rhinoceros tooth protein sequence from Georgia, which was analyzed in 2019. Although, the protein is harder and can survive in fossils. very old from places without permafrost, it is not as useful as DNA for researchers who want to study the ancestry of an organism.
This is just one of the reasons why the new mammoth DNA study is so important: it contains genetic information that has not been available in older protein samples.
A second reason the study reports is that it has beaten the ancient DNA of a 560,000- to 780,000-year-old horse-legged bone genome found in Yukon Territory, Canada, by sequence. of older DNA. Considering the age of the mammoth specimens, Dalén said:
“This DNA is incredibly old. The samples are a thousand times older than the Viking remains, and even predate the existence of humans and Neanderthals“.
The first example of hybrid speciation in ancient DNA
The new study has also expanded the ability of researchers to track the evolutionary process of speciation: the formation of new and different species. A Nature the press release indicates that this process generally occurs “in periods of time that are believed to be beyond the limits of DNA research.”
A tusk of a woolly mammoth discovered in a bed of streams on Wrangel Island in 2017. (Credit: Love Dalén)
However, scientists’ study of mammoth DNA suggests that there was not one, but two different mammoth lineages alive during the early Pleistocene in the region of present-day eastern Siberia. Adycha and Chukochya are believed to be members of a species that bred the woolly mammoth, but Krestovka appears to have come from an unknown and possibly completely new lineage of mammoths. Tom van der Valk, lead author of the study and bioinformatics at Uppsala University in Sweden, explains the shock of researchers at this discovery:
“It simply came to our notice then. All previous studies have indicated that there was only one species of mammoth in Siberia at that time, called the steppe mammoth. But our DNA analyzes now show that there were two different genetic lineages, which here we call the Adycha mammoth and the Krestovka mammoth. We still can’t say for sure, but we think they can represent two different species. ”
In their study, researchers suggest that the Krestovka genome may have diverged from other mammoths between 2.66 and 1.78 million years ago. They also believe that this lineage of mammoths “was ancestral to the first mammoths that colonized North America.” It seems that American Colombian mammoths ( Mammuthus columbi ) can trace half their ancestry to woolly mammoths and half to the Krestovka mammoth lineage that was not known.
He Nature A news report states that this means that the new study has also provided the first evidence of “hybrid speciation,” a new species that is formed by mixing, which is found in ancient DNA. The study’s co-director, Patrícia Pečnerová, an evolutionary biologist at the Swedish Museum of Natural History, says the team believes that “the Colombian mammoth, one of the most emblematic species of the Ice Age of North America, evolved through a hybridization that took place approximately. 420,000 years ago. ”
How far can researchers go?
Finally, the ancient study of mammoth DNA has inspired Dalén to analyze more samples of permafrost animals dating back more than a million years. Next on your list? Oxen, moose and fly lemmings. But the professor of evolutionary genetics knows that there is an age limit that he will not be able to cross when analyzing ancient DNA – 2.6 million years – “This is the limit of permafrost. It used to be too hot, ”he says.
Woolly mammoth tusk emerging from the permafrost on the central island of Wrangel, located in northeastern Siberia. (Credit: Love Dalén)
Top image: The illustration depicts a reconstruction of the steppe mammoths that preceded the woolly mammoth, based on the genetic knowledge we now have of the Adycha mammoth. Source: Beth Zaiken / Center for Paleogenetics
By Alicia McDermott